This image shows only the swells directed at Balephetrish (Tiree) that coincided with light winds or offshore conditions through a typical northern hemisphere winter. It is based on 6931 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. Green and yellow illustrate increasing swell sizes and red shows the largest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how often that size swell was forecast.

The diagram indicates that the prevailing swell direction, shown by the biggest spokes, was W, whereas the the most common wind blows from the SW. The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 35% of the time, equivalent to 32 days. Expect open water swells to exceed >3m (>10ft) 13% of the time (12 days). Taking into account the ratio of these swells that coincided with predicted offshore winds, and given the fact that Balephetrish (Tiree) is exposed to open water swells, we think that that clean surf can be found at Balephetrish (Tiree) about 35% of the time and that surf is blown out by onshore wind 44% of the time. This is means that we expect 72 days with waves in a typical northern hemisphere winter, of which 32 days should be surfable.

IMPORTANT: Beta version feature! Swell heights are open water values from NWW3. There is no attempt to model near-shore effects. Coastal wave heights will generally be less, especially if the break does not have unobstructed exposure to the open ocean.